Brain & Focus
7 mental math tricks to calculate faster in your head
Fast mental math isn't a gift — it's a small bag of shortcuts plus enough practice that you reach for them without thinking. Here are seven that cover most everyday calculations.
The shortcuts
1Add left to right, not right to left: 47 + 36 → 70, then 13 → 83. Fewer carries to hold in your head.
2Round and adjust: 198 + 47 → 200 + 47 − 2 = 245.
3Multiply by 5 by halving and ×10: 86 × 5 → 86 ÷ 2 = 43 → 430.
4Multiply by 9 with ×10 minus the number: 9 × 7 → 70 − 7 = 63.
5Square numbers ending in 5: 35² → 3×4 = 12, tack on 25 → 1225.
6Percentages flip: 8% of 50 equals 50% of 8 = 4. Often the flipped version is trivial.
7Estimate first: get the rough answer, then refine. It catches big mistakes instantly.
Speed comes from recognising which trick fits — and that only happens with reps.
Knowing the tricks is step one; making them automatic is step two. Speed games like Math Blitz and Number Rush in Cognito are built for exactly that — short bursts that turn “I could work that out” into “I just know it.”
